Wood bending and forming

History Since the 1830s, when Michael Thonet began producing laminated and steam-bent chairs in Europe, manufacturers and designers have explored the design and economic advantages of "bentwood."

Veneer Laminating: In the 1940s, several Canadian designers and manufacturers started producing revolutionary laminated and formed-plywood furniture using technology developed for aircraft production during World War II. These included Jack White (Mouldcraft, Vancouver), Peter Cotton (Pion Ornamental Iron, Vancouver), Hugh Dodds and Lawrie Mackintosh (Aero Marine Industries, Oakville), Waclaw Czerwinski and Hilary Stykolt (Canadian Wooden Aircraft, Stratford), Archibald King and Balfour Swim (Ven-Rez Products, Shelburne). (See History of Canadian Contemporary Furniture Design and below for these and other examples.)

Bentwood images  »» enlarge

With growing worldwide interest in contemporary furniture, designers are again experimenting with wood-forming technologies to give their furniture lines a uniqueness to combat the leveling forces of globalization.

Designer/makers can build their own moulds or purchase a range or standard shapes/components from suppliers (see sidebar).

Veneer laminating moulds

The term "laminated" refers to furniture components where the veneer's grain is uni-directional. In "formed plywood" the veneer's grain alternates. Curved components are created when muliple layers of veneer and adhesive are assembled in moulds and pressure is applied. A male and female mould [1] is typically used for production of larger quantities of laminated or formed-plywood parts. The mould is constructed from identical layers of routed (or CNC machined) synthetic panel material bolted together like a giant multi-layer sandwich held together with toothpicks. The male former mould [2] is used for short runs or prototyping.

Veneer laminating moulds

The steel band former mould [3] is less costly to produce than male and female moulds and can apply considerable pressure to the glue line. The pressure hose mould [4] uses a flexible hose (fire hose is often used) to force the veneer against the main rigid former. (Any mould subjected to high pressure should be substantially constructed and inspected by an engineer before use.) For more information, see sidebar and Wood Bending Handbook (part B).

Minimum radii thin laminations (veneer) (1)

Species (Botanical Name) RadiusRatio:

Alder Alnus glutinosa188 mm59
Ash (UK) Fraxinus excelsior122 mm38
Douglas-fir (UK) Pseudotsuga menziesii198 mm62
Poplar (France) Populus sp.160 mm50
White Elm Ulmus americana109 mm34
Western Hemlock (UK) Tsuga heterophylla223 mm70
American White Oak Quercus spp.137 mm43
Walnut (UK) Juglans regia91 mm29

Solid wood steaming With the application of heat and moisture, solid wood becomes more pliable. In this state it can be shaped with the aid of various types of jigs that allow pressure to be applied until the wood cools and/or dries. Pliability is achieved by placing the wood in a "steam chamber" and subjecting it to saturated steam (100 degrees C) at atmospheric pressure. As the best results are obtained with wood that is thoroughly heated, apply the heat for about two minutes per millimetre of thickness.

Steam bending mould

To produce a common U-shaped bend, sandwich the steamed component with a flexible steel strap and make the assembly taut by applying pressure with adjustable end stops. Then centre the assembly on the crown of the form and use the two handles to bring the component to the final position, as shown in the diagram above. For more information, see Wood Bending Handbook (part A), Bending Solid Wood to Form by Edward Peck and this YouTube video.

Minimum radii steam-bent wood (2)

Species (Botanical Name) Strap SupportedUnsupported

Alder Alnus glutinosa360 mm460 mm
American Ash Fraxinus sp.110 mm330 mm
Douglas-fir (UK) Pseudotsuga menziesii460 mm840 mm
Poplar (France) Populus sp.810 mm660 mm
Canadian Yellow Birch (*) Betula alleghaniensis76 mm430 mm
White Elm Ulmus americana43 mm340 mm
Western Hemlock (UK) Tsuga heterophylla480 mm910 mm
American White Oak Quercus spp.13 mm330 mm
Walnut (UK) Juglans regia25 mm280 mm

Steam-Bending Instruction Booklet

Curved Plywood
Canadian report Curved Plywood - Report 177 by D. G. Miller. Available in a few Canadian libraries, this (1962) Department of Forestry twelve-page report gives a brief overview of the application of "bonded curved plywood" in the furniture industry.

Source of data Wood Bending Handbook by W.C. Stevens and N. Turner

(1) Test sample 3.2mm thick and 12 percent moisture content

(2) Test sample 25.4mm thick and air-dried

(*) small-scale test

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